Основы теории английского языка. Листунова Е.И. - 56 стр.

                 Noun-Characteristics of the Infinitive

      The infinitive has the following syntactical characteristics of a noun:
      a) It may be used as the subject of the sentence:
      ...To tramp for three hours through fluffy snow exhausted him
(L. Sinclair). To talk of those merry school-days makes one young
again (Dickens);
      b) It may have the function of an object:
      ...She had promised to take Florrie with her... (Cronin). He
helped me to alight from the carriage (Bronte). I’m sorry to keep you
up so late (Voynich).

                  The Particle to before the Infinitive

      1. In Modern English the infinitive is usually preceded by the
particle to. Formerly this to was a preposition which was put before the
infinitive (then a noun in the dative case) to indicate direction or
purpose. In the course of time to lost its meaning of direction or
purpose, and became merely the sign of the infinitive. But in some
cases it has still preserved its old meaning of purpose.
      Compare:
      I like to read. I went to the library to read (purpose). I want to
stop here. Everything was done to stop (purpose) the fire. He wan-
dered back to the house to look for his mother (Lawrence). She had
turned her head to speak to her boy... (Galsworthy).
      2. The infinitive is used without to in the following instances
(instances «b», «c», «d», «e» refer to cases when the infinitive is part
of a complex object):
      a) After the auxiliary and modal (defective) verbs shall, will,
do, may, can, must:
      I must go and look at the flowers at Hampton Court. Will you
come? (Aldington). «May I have a cigarette?» he asked (Conrad).
      But after the modal (defective) verb ought the infinitive is al-
ways used with to:
      I ought to have done it (Locke). You ought to see her (Lawrence).
      b) After some verbs expressing physical perceptions: to hear, to
see, to feel, to perceive:
      ...They felt the boat shudder as its speed slackened (Cusack).
...He heard a blackbird sing (Galsworthy). He saw Irene come in, pick
up the telegram, and read it (Galsworthy).
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